Resonance Linewidth and Line Narrowing in the Photoionization Spectrum of Sodium Atom in AN Electric Field.

S. Feneuille, Sylvain Liberman, Eliane Luc-Koenig +2 more

J.-Y. Liu, Patrick J. McNicholl, David A. Harmin +3 more

We have observed a striking line narrowing in the photoionization spectrum of sodium atoms in an electric field. At crossings of two relatively broad resonances, one of them is narrowed by 2 to 3 orders of magnitude as a result of interference between the discrete and continuum coupling amplitudes that mediate their ionization. The observations agree quantitatively with WKB quantum-defect Stark theory and also with a simpler model involving two discrete states and two continua.

Nikolai V. Fateev

Eugeny N. Kotlikov, L. Yu. Khryashchev

D. B. Tretyakov, Ilya I. Beterov, V. M. Entin +7 more

Experiments are carried out on the spectroscopy of the Förster resonance lines Rb(37 P ) + Rb(37 P ) → Rb(37 S ) + Rb(38 S ) and microwave transitions nP → n ′ S , n ′ D between Rydberg states of cold rubidium atoms in a magneto-optical trap (MOT). Under ordinary conditions, all spectra exhibit a linewidth of 2–3 MHz irrespective of the interaction time between atoms or between atoms and microwave radiation, although the limit resonance width should be determined by the inverse interaction time. The analysis of experimental conditions has shown that the main source of line broadening is the inhomogeneous electric field of cold photoions that are generated under the excitation of initial nP Rydberg states by broadband pulsed laser radiation. The application of an additional electric-field pulse that rapidly extracts photoions produced by a laser pulse leads to a considerable narrowing of lines of microwave resonances and the Förster resonance. Various sources of line broadening in cold Rydberg atoms are analyzed.

Scott H. Bloom, Eric J. Korevaar, M. Rivers +1 more

An experimental demonstration of a fast atomic line filter/field ionization detector (FALF/FID) is presented. The FALF/FID detects incoming signal photons by resonant absorption in an atomic vapor cell containing a strong electric field. Excited atoms are electric-field ionized after further excitation to a Stark-shifted Rydberg level by a pump laser tuned to a resonance in the ionization spectrum, providing an observed enhancement in the ionization rate of ten times over the continuum ionization threshold. Preliminary measurements of time response (<10 nsec) and quantum efficiency (>25%) indicate that with optimization the FALF/FID will provide high quantum efficiency, fast time response, and narrow-linewidth detection.